| The LIBNAME Statement for PC Files on Microsoft Windows |
Controls the format of the WHERE clause when you use the DBKEY=
data set option.
| Valid in: |
DATA and PROC steps (when accessing PC files
data using SAS/ACCESS software)
|
| Default value: |
LIBNAME setting
|
If there might be NULL values in the transaction
table or the master table for the columns that you specify in the DBKEY= option, then use DBNULLKEYS=YES. When you specify
DBNULLKEYS=YES and specify
a column that is not defined as NOT NULL in the DBKEY= data set option, SAS
generates a WHERE clause that can find NULL values. For example, if you specify
DBKEY=COLUMN and COLUMN is not defined as NOT NULL, SAS generates a WHERE
clause with the following syntax:
WHERE ((COLUMN = ?) OR ((COLUMN IS NULL) AND (? IS NULL)))
This syntax enables SAS to prepare the statement once and use it for
any value (NULL or NOT NULL) in the column. Note that this syntax has the
potential to be much less efficient than the shorter form of the WHERE clause
(presented below). When you specify DBNULLKEYS=NO or specify a column that
is defined as NOT NULL in the DBKEY= option, SAS generates a simple WHERE
clause.
If you know that there are no NULL values in the transaction
table or the master table for the columns that you specify in the DBKEY= option,
you can use DBNULLKEYS=NO. If you specify DBNULLKEYS=NO and specify DBKEY=COLUMN,
SAS generates a shorter form of the WHERE clause--regardless of whether
the column that DBKEY= specifies is defined as NOT NULL:
WHERE (COLUMN = ?)
To assign this option to a group of tables, use the
DBNULLKEYS= option specified in LIBNAME Options for PC Files on Microsoft Windows.
Copyright © 2007 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
